The present invention relates to compressors and controls valves for compressors, and more particularly, to variable displacement compressors and control valves employed in such compressors.
A typical type of variable displacement compressor employs an inclinable drive plate housed in a crank chamber. The inclination of the drive plate is changed to vary the displacement of the compressor. A control valve adjusts the pressure in the crank chamber (crank pressure Pc) to alter the inclination of the drive plate. Japanese Unexamined Patent Publication No. 6-26454 describes a compressor that employs such a control valve. The compressor has a bleeding passage that connects a crank chamber to a suction chamber (which is connected to the outlet of an evaporator). The control valve is located in the bleeding passage and includes an electromagnetic coil, a bellows, a valve body attached to the bellows, a valve chamber accommodating the bellows and the valve body, and a valve port connecting the crank chamber and the suction chamber. The target of the pressure in the suction chamber (target suction pressure) is adjusted by changing the current flowing through the electromagnetic coil. The refrigerant gas in the suction chamber is drawn into the valve chamber. The pressure of the suction chamber (suction pressure Ps) communicated to the valve chamber moves the valve body and changes the opened area of the valve port. This adjusts the amount of refrigerant gas that is released into the suction chamber from the crank chamber and thus controls the crank pressure Pc. The force of the bellows acts on the valve body to close the valve port, while the crank pressure Pc acts on the valve body to open the valve port.
In automobile air-conditioning systems, clutchless variable displacement compressors are often employed since they are lighter than compressors having clutches. A clutchless compressor is directly connected to an external drive source, or engine, by a pulley and a transmission belt without using an electromagnetic clutch. Since engine power is constantly transmitted to the compressor, the displacement of the compressor must be minimized by moving the drive plate to a minimum inclination position when the passenger compartment does not require cooling or when the cooling load is extremely small.
The control valve described in the Japanese patent publication can be employed in a clutchless variable displacement compressor. However, it is rather difficult to maintain the drive plate at the minimum inclination position and operate the compressor in a minimum displacement state. This is because the control valve must be either completely closed or minimally opened to maximize the crank pressure Pc and hold the drive plate at the minimum inclination position. Since the crank pressure Pc acts to open the control valve, it becomes difficult to keep the control valve closed or minimally opened as the crank pressure Pc increases. As a result, the crank pressure Pc cannot be increased sufficiently to hold the drive plate at the minimum inclination position and maintain minimum displacement operation. If minimum displacement cannot be continued when cooling is not necessary, engine power is consumed by the compressor in an inefficient manner. This diminishes the merits of clutchless compressors.
Accordingly, it is an objective of the present invention to provide a control valve that regulates the release of gas from a crank chamber in a clutchless variable displacement compressor. It is a further objective of the present invention to provide a clutchless variable displacement compressor that can continue minimum inclination operation as long as necessary.
To achieve the above objectives, the present invention provides a control valve for use with a compressor. The compressor is generally of the type that has a drive plate that inclines with respect to the axis of a drive shaft. The drive plate connects a piston to the drive shaft to convert rotation of the drive shaft into linear reciprocation of the piston within a cylinder bore. The compressor has a crank chamber which accommodates the drive plate. The pressure of the crank pressure is a crank pressure. The compressor also has a suction chamber into which gas is introduced from an external refrigerant circuit. The pressure of the suction chamber is a suction pressure. The compressor also includes a bleeding passage that permits flow of gas from the crank chamber to the suction chamber. Displacement of the compressor is varied depending on the inclination of the drive plate, which varies depending on the crank pressure.
In one aspect of the present invention, a control valve includes a valve chamber that forms a part of the blending passage. A valve seat defines a crank chamber side region and a suction chamber side region in the valve chamber. A valve port is formed in the valve seat to connect the two regions. A valve body engages and disengages from the valve seat to close and open the valve port, respectively. The control valve also includes a force transferring member. One of the valve body and the force transferring member is located in the crank chamber side region while the other is located in the suction chamber side region. A first spring urges the valve body toward the valve seat. A solenoid assembly generates an electromagnetic biasing force that is dependent upon the level of an electric current supplied to the solenoid assembly. The solenoid assembly urges the valve body in a direction away from the valve seat in accordance with the biasing force. The valve body remains engaged with the valve seat to close the valve port, regardless of the crank pressure or the suction pressure, when no electric current is supplied to the solenoid assembly.
This aspect of the present invention facilitates minimum displacement operation of the compressor for a desired period of time and therefore makes the valve suitable for a clutch-less type compressor that is directly connected to an engine with a belt and/or a pulley.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.